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View Full Version : smooth ball diff rebuild... how?


Tjay
2008.03.03, 03:57 PM
Ok, I have been running my awd for almost a month now and have gone through 2 sets of atomic plastic ball diffs. On Saturday afternoon, my car was running great and at night the rear end started spinning out and car's traction rolling on the sweeper.

Last night I noticed my rear atm plastic dif was locking up. Only when you're pushing the car with your finger (keep in mind the pinion is not there). The right rear locks up and it feels like it's snapping. I checked the swing-shaft, spur gear, knuckles and bearing and they're all in good condition. Visually, I can't see anything wrong with the diff but trying to hand spin the diff it feels gritty and locks up half way through. I have tried rebuilding some of my atm plastic diffs and after you open them and put them together they don't feel as smooth anymore.

I don't want to keep buying new atm diffs. So, is there any way to rebuild this diff and still keep it's smoothness? Maybe invest into ceramic and thrust bearing? I don't mind investing into kyosho diffs if they'll last longer.

Please advice.

thx!

ruf
2008.03.03, 04:08 PM
Tjay - chances are the issue is in the thrust bearing. Try the Atomic flat thrust bearing. I'm also working on a conversion using Kyosho ball diff guts including their thrust bearing. Aside from that, use the standard diff building techniques like sanding the rings. Also based on your description of the problem, the issue may not be with the diff internals, but the diff gear.

EMU
2008.03.03, 04:55 PM
Using the upgrade flat thrust bearing makes a big difference. Since the pressure is loaded from the side of the bearing, the standard ball bearing is not really designed for that type of pressure. Made my diff much smoother.

ruf
2008.03.03, 05:01 PM
There is a quick way to tell whether the grit is in your thrust bearing:
1) Rotate both sides of the diff with both hands to get a feel for the level of wear/roughness.
2) Apply sideways pressure to diff halves (you can do this with the diff installed on the MR-02, but you'll have to remove it for AWD). This unloads the thrust bearing so all you are feeling is the rings/balls.
3) Keep applying pressure and rotate both sides of the diff. Try and feel if the diff feels better/smoother or just as rough.

Chances are that the diff feels perfectly smooth in #3. This means that your rings and balls are fine, but your thrust bearing is shot. If the diff is still crunchy in #3, then your rings and balls are the culprit, and you probably just need to resurface your rings - especially if you are using ceramic balls. If it's kind of halfway better in #3, then rings, balls, and thrust bearing are worn out.

BTW, a quick trick for trackside rebuilds when you don't have access to another conventional bearing is to flip it. The races are only worn on one set of opposite sides, so there SHOULD be a fresh set of races under pressure if you reinstall it the other way around. Should buy you a little more time unless the bearing is just completely shot.

mk2kompressor
2008.03.03, 05:19 PM
BTW, a quick trick for trackside rebuilds when you don't have access to another conventional bearing is to flip it. The races are only worn on one (opposite) side, so there SHOULD be a fresh set of races under pressure if you reinstall it the other way around. Should buy you a little more time unless the bearing is just completely shot.


^very good tip!!^

the ceramic balls do make a big difference,ive had my atm plastic diffs in for half a year now with no probs,just the adjusting nut wearing a little from stripping the diff all the time lol
the holes in the new thrust bearings are a little too big allowing the diff gear to move up and down,its ok whilst running just something to watch out for when you build them up:)

Tjay
2008.03.03, 05:34 PM
Thanks for the tip guys!

Still too new to AWD :). I haven't seen how a thrust bearing looks like... I'll look at it later on at the shop and see how this thing works. For the mean time, I'll do all that testing and then change the standard balls to ceramic.

Tjay
2008.03.03, 05:44 PM
Thanks for the tip guys!

Still too new to AWD :). I haven't seen how a thrust bearing looks like... I'll look at it later on at the shop and see how this thing works. For the mean time, I'll do all that testing and then change the standard balls to ceramic.


Just did some research and found out mine suppose to come with thrust bearing... I'll have to check it.

Gigibesi
2008.03.07, 03:01 AM
can i know how tight should i screw the ATM ball diff together when i reassemble the diff? Should i tighthen the diff completly then slowly adjust later or other wise?

Tjay
2008.03.07, 11:27 AM
what I usually do, is to tighten it all the way then back off 1/2 a turn. It seems a lot but put the car on the track and check to see if the diff slips by going in full reverse then full throttle. I have mine to were it slips a little. Others may have different way of doing it.

Tjay
2008.03.07, 11:28 AM
Just did some research and found out mine suppose to come with thrust bearing... I'll have to check it.

update: mine don't come with thrust bearing. I have to get that tonight.

andreophile
2008.03.07, 12:00 PM
put the car on the track and check to see if the diff slips by going in full reverse then full throttle.

Won't the drivetrain be severely damaged by doing that?

Tjay
2008.03.07, 12:12 PM
it will slip... if it was a solid axle, gear diff, super glued pinion shaft and super glued spur. Yes, it will.

simalive
2008.03.07, 12:56 PM
On a side note, I wish all the diff have measurement markings printed on them, so you know exactly how tight it is, and how much it has loosen since your last adjustments.

neweraz84
2008.03.07, 01:35 PM
this is so weird, i had the same problem with my stock gear diff after 4 months. I took it apart and put it back together and still nothing. I guess this happens every now and then, thought i was the only one to experience the problem.

ruf
2008.03.07, 02:02 PM
I just tighten by hand/feel. After you've done a few of these, you'll get an idea of how tight they need to be. You want to BARELY be able to slip the diff gear while holding both sides. In fact, I do this to help seat the balls in freshly prepped rings. Then work the diff action again and retighten since it usually loosens up a little.

simalive - you could easily use a paint pen to make witness marks, but it wouldn't really help much. Most of the time, diffs "loosen" due to the balls and rings etc. breaking in, NOT from the adjustment nut backing out. You could mark your adjustments, but they wouldn't move (esp if you use loctite), and there's no way to mark the internal wear that's causing the diff to loosen.

CristianTabush
2008.03.09, 01:35 PM
Quote:
Originally Posted by Tjay View Post
put the car on the track and check to see if the diff slips by going in full reverse then full throttle.
Won't the drivetrain be severely damaged by doing that?

Yes it will, no matter if you have ball diffs or not. TJ, this is NOT THE WAY to check your ball diff. :eek: It is probably one of the reasons why your diffs were cooked. This is especially hard on the center spur gear.

Gigibesi
2008.03.10, 12:12 PM
Quote:
Originally Posted by Tjay View Post
put the car on the track and check to see if the diff slips by going in full reverse then full throttle.
Won't the drivetrain be severely damaged by doing that?

Yes it will, no matter if you have ball diffs or not. TJ, this is NOT THE WAY to check your ball diff. :eek: It is probably one of the reasons why your diffs were cooked. This is especially hard on the center spur gear.

actually is there any other proper way of check ball diff if it was sliping other than holding the ends and check? i

CristianTabush
2008.03.10, 12:29 PM
Best way to check them is by hitting the gas. If your car accelerates well and you can't hear differential slippage then the rear differential is tight enough. For the front, I adjust it according to steering characteristics. If I want more initial turn-in, I run it looser. If it is too loose, the car will be sluggish and unstable coming out of the corner, wanting to almost swap ends as the rear will over drive the front badly. If it is too tight, the car won't turn initially. I tend to like a fairly tight diff in the front so that the car gets pulled out of the corner with the front rather than pushed by the rear.

Tjay
2008.03.10, 12:35 PM
Yes it will, no matter if you have ball diffs or not. TJ, this is NOT THE WAY to check your ball diff. :eek: It is probably one of the reasons why your diffs were cooked. This is especially hard on the center spur gear.

Thanks for the tip Christian. This is what I have learned and I think 99% of us that races here do it this way. I'll have to let those guys know as well.